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The letter right after $\subset$.

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AboAmmar
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manofbear
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1 Answers1

4

It is a \mathscr{S}

enter image description here

\documentclass[12pt, border=2pt]{standalone}
\usepackage{mathrsfs}
\begin{document}
$\{T_n\}_{n=1}^{\infty}\subseteq\mathscr{S}_a$
\end{document}
marsupilam
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